// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/message_loop/message_pump_default.h"

#include <algorithm>

#include "base/logging.h"
#include "base/threading/thread_restrictions.h"
#include "build/build_config.h"

#if defined(OS_MACOSX)
#include "base/mac/scoped_nsautorelease_pool.h"
#endif

namespace base {

MessagePumpDefault::MessagePumpDefault()
    : keep_running_(true)
    , event_(WaitableEvent::ResetPolicy::AUTOMATIC,
          WaitableEvent::InitialState::NOT_SIGNALED)
{
}

MessagePumpDefault::~MessagePumpDefault()
{
}

void MessagePumpDefault::Run(Delegate* delegate)
{
    DCHECK(keep_running_) << "Quit must have been called outside of Run!";

    for (;;) {
#if defined(OS_MACOSX)
        mac::ScopedNSAutoreleasePool autorelease_pool;
#endif

        bool did_work = delegate->DoWork();
        if (!keep_running_)
            break;

        did_work |= delegate->DoDelayedWork(&delayed_work_time_);
        if (!keep_running_)
            break;

        if (did_work)
            continue;

        did_work = delegate->DoIdleWork();
        if (!keep_running_)
            break;

        if (did_work)
            continue;

        ThreadRestrictions::ScopedAllowWait allow_wait;
        if (delayed_work_time_.is_null()) {
            event_.Wait();
        } else {
            TimeDelta delay = delayed_work_time_ - TimeTicks::Now();
            if (delay > TimeDelta()) {
#if defined(OS_WIN)
                // TODO(stanisc): crbug.com/623223: Consider moving the OS_WIN specific
                // logic into TimedWait implementation in waitable_event_win.cc.

                // crbug.com/487724: on Windows, waiting for less than 1 ms results in
                // returning from TimedWait promptly and spinning
                // MessagePumpDefault::Run loop for up to 1 ms - until it is time to
                // run a delayed task. |min_delay| is the minimum possible wait to
                // to avoid the spinning.
                /*constexpr*/ TimeDelta min_delay = TimeDelta::FromMilliseconds(1);
                do {
                    delay = std::max(delay, min_delay);
                    if (event_.TimedWait(delay))
                        break;

                    // TimedWait can time out earlier than the specified |delay| on
                    // Windows. It doesn't make sense to run the outer loop in that case
                    // because there isn't going to be any new work. It is less overhead
                    // to just go back to wait.
                    // In practice this inner wait loop might have up to 3 iterations.
                    delay = delayed_work_time_ - TimeTicks::Now();
                } while (delay > TimeDelta());
#else
                event_.TimedWait(delay);
#endif
            } else {
                // It looks like delayed_work_time_ indicates a time in the past, so we
                // need to call DoDelayedWork now.
                delayed_work_time_ = TimeTicks();
            }
        }
        // Since event_ is auto-reset, we don't need to do anything special here
        // other than service each delegate method.
    }

    keep_running_ = true;
}

void MessagePumpDefault::Quit()
{
    keep_running_ = false;
}

void MessagePumpDefault::ScheduleWork()
{
    // Since this can be called on any thread, we need to ensure that our Run
    // loop wakes up.
    event_.Signal();
}

void MessagePumpDefault::ScheduleDelayedWork(
    const TimeTicks& delayed_work_time)
{
    // We know that we can't be blocked on Wait right now since this method can
    // only be called on the same thread as Run, so we only need to update our
    // record of how long to sleep when we do sleep.
    delayed_work_time_ = delayed_work_time;
}

} // namespace base
